So at this point, I'd like to see if anyone would be able to make a threaded knob for the pistol, as a lever action would be too many moving parts. The trick I think would be having enough of a grip to quickly turn it to let loose the 12g since the barrel extension hangs out like it does in the first picture.

Here is the picture as requested in better lighting, Superman. How it's supposed to be is in the first image in the thread, where it was still on the gun and not in pieces. rednecksniper was the original designer of the lever, and unfortunately he is no longer around

I have a similar home-brew lever changer. There would have been a small brass wheel on an axle/pin in that front-most forked piece. When you close the changer to pierce a 12ie, the wheel would ride on the cammed section of the lever. A longer than average co2 cartridge probably broke the pin and the wheel fell out, lot of torque going through that small piece. I think that's why the pierce pin on other lever changers (ICD for instance) is spring loaded - so longer cartridges don't stress out the mechanism.